The goals of Project 2 are to examine the immunobiology of human TIM proteins. We recently discovered the Tim (T cell-lmunoglobulin-Mucin) genes, which we showed, regulate the development of murine asthma and Th2 cytokine production. The human TIM gene family consists of three closely linked genes on chromosome 5q33.2, a region repeatedly linked to the development of asthma, and both the human and mouse Tim locus are highly polymorphic. In addition, human TIM-1 is the receptor for hepatitis A virus (HAV), suggesting that CD4 T cells and TIM-1 may mediate the known protective effect of prior infection with HAV on the development of atopy. In Specific Aim 1, we will determine what cell types express TIMs, and the kinetics of this expression using anti-TIM mAb and quantitative RT-PCR analysis. We believe that TIMs critically regulate T cell differentiation, as evidenced by the fact that TIM-1 is preferentially expressed on Th2 cells, and by the fact that TIM-3 is preferentially expressed on Th1 cells. Thus, by identifying when and where TIMs are expressed we will obtain essential information about, and clues regarding, human TIM function. In Specific Aim 2, we will utilize TIM blocking reagents (Ig fusion proteins and mAbs) to directly study the precise role of TIM-1 and TIM-3 in the development of Th2 responses, in T helper differentiation and in myeloid cell activation. In addition, we will examine the costimulatory function of TIMs in T cell activation. In Specific Aim 3, we will molecularly clone the ligand for TIM-1 and TIM-3 by COS cell expression cloning using TIM-1-lg and TIM-3-1g fusion proteins to identify the ligands for TIM-1 and TIM-3 by expression cloning. Identification of the TIM-1 and TIM-3 ligands will provide us with a greater understanding of the mechanisms by which TIM/TIM-ligand pathways regulate T cell differentiation and the development of atopy. These studies together will greatly increase our understanding of the function of TIMs in the regulation of human Th2 responses, and will characterize a crucial regulator of CD4 T cell differentiation and a novel and extremely important asthma susceptibility gene that we have recently discovered.